however, killing the catastrophic well off is a bittersweet victory for gulf coast residents, who fear they'll be battling the effects of the nation's worst environmental disaster for years to come. nbc's jay greg has our report. >> reporter: it began april 20th with a massive fireball and deadly flames cutting through the night air. as the deepwater horizon rig exploded, then collapsed, 11 lives were lost. and oil began to seep into the gulf, the start of the worst spill in u.s. history. now, 154 days later, government scientists say the final seal, 74 barrels of cement, is holding tight, and that the well will never leak again. president obama acknowledged the work that's been done and perhaps the more difficult job that lies ahead, in a written statement which says, in part, we will continue to work closely with the people of the gulf to rebuild their livelihoods and restore the environment that supports them.